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    <title>ShellCheck: SC3028 – In POSIX sh, VARIABLE is undefined.</title>
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    <h1>SC3028 – ShellCheck Wiki</h1>
    <a href="https://github.com/koalaman/shellcheck/wiki/SC3028">See this page on GitHub</a>
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    <h2 id="in-posix-sh-variable-is-undefined">In POSIX sh, VARIABLE is
undefined.</h2>
<p>(or "In dash, ... is not supported." when using
<code>dash</code>)</p>
<h3 id="problematic-code">Problematic code:</h3>
<div class="sourceCode" id="cb1"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb1-1"><a href="SC3028.html#cb1-1" aria-hidden="true" tabindex="-1"></a><span class="co">#!/bin/sh</span></span>
<span id="cb1-2"><a href="SC3028.html#cb1-2" aria-hidden="true" tabindex="-1"></a><span class="bu">echo</span> <span class="st">&quot;</span><span class="va">$HOSTNAME</span><span class="st"> </span><span class="va">$UID</span><span class="st"> </span><span class="va">$RANDOM</span><span class="st">&quot;</span></span></code></pre></div>
<h3 id="correct-code">Correct code:</h3>
<p>Either switch to a shell like <code>bash</code> that supports the
special variable you're trying to use, or use an external command to get
the information you want:</p>
<div class="sourceCode" id="cb2"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb2-1"><a href="SC3028.html#cb2-1" aria-hidden="true" tabindex="-1"></a><span class="co">#!/bin/sh</span></span>
<span id="cb2-2"><a href="SC3028.html#cb2-2" aria-hidden="true" tabindex="-1"></a><span class="bu">echo</span> <span class="st">&quot;</span><span class="va">$(</span><span class="fu">hostname</span><span class="va">)</span><span class="st"> </span><span class="va">$(</span><span class="fu">id</span> <span class="at">-u</span><span class="va">)</span><span class="st"> </span><span class="va">$(</span><span class="fu">awk</span> <span class="st">&#39;BEGIN { srand(); print int(rand()*32768) }&#39;</span> /dev/null<span class="va">)</span><span class="st">&quot;</span></span></code></pre></div>
<h3 id="rationale">Rationale:</h3>
<p>The variable you are attempting to use is a special variable in bash
or ksh. To get the same information from <code>dash</code> or POSIX
<code>sh</code>, use an external command instead.</p>
<p>For <code>PIPESTATUS</code>, the pipeline can be instrumented to
record the exit value of each command:</p>
<div class="sourceCode" id="cb3"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb3-1"><a href="SC3028.html#cb3-1" aria-hidden="true" tabindex="-1"></a><span class="kw">{</span> <span class="ex">cmd0</span><span class="kw">;</span> <span class="bu">echo</span> <span class="va">$?</span> <span class="op">&gt;</span> status0<span class="kw">;</span> <span class="kw">}</span> <span class="kw">|</span> <span class="kw">{</span> <span class="ex">cmd1</span><span class="kw">;</span> <span class="bu">echo</span> <span class="va">$?</span> <span class="op">&gt;</span> status1<span class="kw">;</span> <span class="kw">}</span> <span class="kw">|</span> <span class="ex">cmd2</span></span></code></pre></div>
<h3 id="exceptions">Exceptions:</h3>
<p>If you only intend to target shells that support this feature, you
can change the shebang to a shell that guarantees support, or <a
href="ignore.html">ignore</a> this warning.</p>
<p>You can use <code># shellcheck disable=SC3000-SC4000</code> to ignore
all such compatibility warnings.</p>
<h3 id="related-resources">Related resources:</h3>
<ul>
<li>Help by adding links to BashFAQ, StackOverflow, man pages, POSIX,
etc!</li>
</ul>
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